1. Field of the Invention
The present invention relates to a sound signal transmitter-receiver, particularly to a sound signal transmitter-receiver which receives a transmitting voice (sound) from a talker to transmit a transmission sound signal to the outside while receiving a reception sound signal from the outside to make a received voice (sound) to the talker.
2. Description of the Related Art
Conventionally, there is known a sound signal transmitter-receiver in which a reception sound signal is received from the outside to make a received voice to a talker while a transmitting voice is received from the talker to transmit a transmission sound signal to the outside. A technique in which the talker easily catches his or her transmitting voice even in a noisy environment and a technique in which the other party easily catches the received voice even in a noisy environment are also proposed.
For example, a configuration disclosed in Japanese Patent Laying-Open No. 09-037380 includes a noise detector attached to an outer wall of a head set; first and second adaptive filters into which an output signal of the noise detector is fed; a transmitting microphone placed near the mouth of the talker; a control speaker placed in an inner wall of the head set; and an error detector placed in the inner wall of the head set, wherein an output signal of the first adaptive filter is subtracted from an output signal of the transmitting microphone, a factor of the first adaptive filter is updated such that the subtracted signal is small, a factor of the second adaptive filter is updated such that an output signal of the error detector is small, the output signal of the second adaptive filter, the subtracted signal, and a receiving signal from a communication device are added and fed into the control speaker, and the subtracted signal is set as a transmitting output signal for the communication device.
Japanese Patent Laying-Open No. 07-240782 discloses a technique in which a transmission sound signal obtained from a transmitting microphone through an A/D converter is transmitted as a sidetone to a receiving-side adder through a variable gain amplifier and the transmission sound signal is added to a received voice. A background noise level in the transmission sound signal is detected by a background noise level detector, and a gain of the variable gain amplifier is controlled according to a detected background noise level, thereby controlling the sidetone level.
Japanese Patent Laying-Open No. 2000-101683 discloses a technique in which a noise/voice separation unit separates the transmission sound signal from a voice input unit into a noise and a transmitting voice, a signal addition unit adds the transmission sound signal from the noise/voice separation unit to a decoded sound signal decoded by a voice decoding unit according to noise power computed by a noise power computing unit. A level control unit controls the level of the decoded sound signal from the signal addition unit according to the ratio of the noise power computed by the noise power computing unit and decoded voice power computed by a decoded voice power computing unit, and a voice output unit performs D/A conversion on the decoded sound signal from the level control unit and supplies the converted sound signal through a speaker.
Japanese Patent Laying-Open No. 05-030177 discloses a sidetone control circuit of a transmitter-receiver including a level computing device that detects a background noise level when the talker does not make a voice, a voice/noise determination device that detects a noise zone of the transmitting signal, and an attenuation amount controller that supplies a control signal so as to increase the attenuation amount of a variable attenuator when the noise zone is at a high noise level.
Japanese Patent Laying-Open No. 08-018630 discloses a noise suppression hand set having a telephone transmitter and a telephone receiver, the hand set including an ear microphone provided in an ear piece surface to detect a sound between the ear piece and the ear, a noise microphone provided in an outer surface of the hand set to detect the noise. A receiving amplifying circuit superimposes the output of the noise microphone on a receiving input such that the noise that flows between the ear and the ear piece surface becomes the minimum. A transmitting amplifying circuit superimposes the output of the noise microphone on a transmitting output such that the noise included in the transmitting signal becomes the minimum.
In addition, Japanese Patent Laying-Open No. 03-147000 discloses a voice input device including two microphone units, means for converting an electric output of each microphone unit into an envelope signal as electric power, means for obtaining a difference signal between the envelope signals, and means for obtaining a voice zone detecting signal of the voice input device using the difference signal output.
However, for example, in the techniques disclosed in Japanese Patent Laying-Open Nos. 09-037380 and 08-018630, because the noise is reduced using the adaptive filter or a noise canceller, an unsteady noise is hardly reduced while a steady noise is highly reduced. In the techniques disclosed in Japanese Patent Laying-Open Nos. 07-240782, 2000-101683, and 05-030177, the talker hardly catches the transmitting voice because the gain of the transmitting voice is also controlled along with the gain of the noise.